REVIEW ARTICLE published: 16 November 2012 doi: 10.3389/fimmu.2012.00339 New perspectives on the ligands and function of the killer cell immunoglobulin-like KIR3DL2 in health and disease

Jacqueline Shaw and Simon Kollnberger* Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Science, Botnar Research Centre, Oxford University, Oxford, UK

Edited by: KIR3DL2/CD158k/p140 is a three domain killer cell immunoglobulin-like receptor incorpo- Jeroen Van Bergen, Leiden University rating cytoplasmic immunoreceptor tyrosine inhibitory motifs, expressed as a disulphide- Medical Center, Netherlands bonded dimer. KIR3DL2 is a framework within the KIR locus and is highly polymorphic, Reviewed by: with 62 allelic variants possibly coding for reported. KIR3DL2 binds to HLA-A3 and - Jeroen Van Bergen, Leiden University Medical Center, Netherlands A11 in a peptide-dependent fashion and to B27 free heavy chain forms. In addition, KIR3DL2 Teresa Bellon, Hospital La Paz Health can also function as an innate for delivery of CpG DNA toTLR9 in NK cells. Research Institute, Spain The increased levels of expression of KIR3DL2 compared with other KIR expressed byT cell *Correspondence: subsets in healthy individuals suggest it may function as a default KIR receptor. KIR3DL2- Simon Kollnberger, Nuffield expressing natural killer (NK) cells and IL17 secreting CD4 T cells have been implicated Department of Orthopaedics, Rheumatology and Musculoskeletal in the pathogenesis of ankylosing spondylitis. Moreover, KIR3DL2 expression delineates Science, Botnar Research Centre, circulating and cutaneous lymphoma T cells in Sézary’s syndrome. Here we discuss how Oxford University, Windmill Road, the unique molecular attributes of KIR3DL2 impact on its function on NK and T cells and Headington, Oxford OX3 7LD, UK. e-mail: simon.kollnberger@ndorms. how this may relate to its role in disease. ox.ac.uk Keywords: ankylosing spondylitis, B272, CpG DNA, HLA-A11, HLA-A3, HLA-B27, KIR3DL2, Sézary’s syndrome

INTRODUCTION KIR3DL2 gene incorporates nine exons. Exons 1–2 encode for sig- KIR3DL2 has the CD designation CD158k. KIR3DL2 has been nal peptide. The D0, D1, and D2 immunoglobulin-like domains, variously referred to as NKAT4, NKAT4a, NKAT4b, and cl- stem, transmembrane, and cytoplasmic tail regions are encoded 5. The extracellular ligand-binding regions of the killer cell by exons 3–5, 6, 7, and 8–9, respectively (Colonna and Samaridis, immunoglobulin-like receptor (KIR) family of which KIR3DL2 is 1995). The D0, D1, D2 domains, stem, and transmembrane a member are arranged in domains with an immunoglobulin-fold regions of KIR3DL2 are 96, 102, 98, 24, and 20 amino like (Ig) structure. KIR are classified based upon how many extra- acids in length, respectively. The cytoplasmic tail of KIR3DL2 is cellular C2-type immunoglobulin-like domains they have (2D for the longest of all KIR3D proteins incorporating 96 amino acids two domains, 3D for three domains) and by the length of their and contains two regulatory immunoreceptor tyrosine inhibitory cytoplasmic domain (L for long-tailed receptors and S for short motifs (ITIMs). ones; Marsh et al., 2003). KIR3DL2*001 is unique among KIR in being expressed as a 140 kDa dimer (p140, Pende et al., 1996). There are two unpaired GENE ORGANIZATION AND ALLELIC VARIATION cysteines in the stem region at positions 302 and 336 which are not The gene for KIR3DL2 is a framework gene within the KIR gene in the D0, D1, and D2 Ig-like domains and which may be involved locus. KIR3DL2 nucleotide sequences are the longest of all KIR in disulphide-bonded dimerization. spanning 16,256 bp in full genomic sequences and cod- Eighty four allelic variants of KIR3DL2 have been reported ing for a 1,368 bp cDNA (reviewed in the IPD-KIR database: of which 62 encode for potential proteins. The relative expres- http://www.ebi.ac.uk/ipd/kir). The genomic sequence comprises sion levels of these different alleles is unknown. Alleles differ many putative regulatory elements, some of which are unique by amino acid substitutions. 48 of the allelic variants differ to the KIR3DL2 gene, suggesting transcriptional regulation dis- in amino acid sequence in the D0 domain or in the region tinct from other KIR genes. These include putative binding sites between the D0 and D1 domains. Whilst the D0 domains of for RUNX, c-myc, p53, and NFκB transcription factors (Trows- KIR3DL1 and KIR3DS1 are similar, the sequence of KIR3DL2 dale et al., 2001; Cichocki et al., 2009). In addition there are also differs significantly in this region. This strongly suggests that the KIR3DL2 allelic variants in non-coding DNA which may have KIR3DL2 D0 domain has an important role to play in binding to effects on gene transcription. ligand.

KIR3DL2 PROTEIN STRUCTURE REGULATION OF KIR3DL2 EXPRESSION KIR3DL2, is expressed as a protein with signal peptide, sequen- A mean of 24.3% [interquartile range (IQR): 18.7–27.7] natural tial D0, D1, and D2 immunoglobulin-like domains, stem and killer (NK) cells express KIR3DL2 in healthy individuals (Chan cytoplasmic tail regions. Similar to other three domain KIRs, the et al., 2005). These levels are similar to the proportions of NK cells

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in healthy individuals that express other KIR for which antibodies function against target cells (Fauriat et al., 2008). This suggests are available such as KIR3DL1. that it is unlikely that self peptides which promote binding of KIR3DL2 is expressed on a higher proportion of CD4 and pMHC complexes of HLA-A3 to KIR3DL2 are naturally more CD8 T cells than other KIR (Chan et al., 2005). We have shown abundant. that a mean of 9% (IQR: 4.6–13.7) peripheral blood CD8 T Residues in the D1 domain of KIR3DL2 are probably critical for cells and 5% CD4 T cells (IQR: 1.8–6) express KIR3DL2 com- recognition of HLA-A11 and -A3 since gene conversion has gener- pared to 0.5 and 1% of CD4 and CD8 T expressing other KIR, ated KIR2DS4 which binds HLA-A11 but has reduced specificity respectively. This suggests that KIR3DL2 expression may be less for HLA-C (Graef et al., 2009). tightly controlled than other KIR. KIR3DL2 expression is enriched HLA-B27 (B27) is expressed at the cell surface of antigen pre- on memory CD45RO+CD28−CCR7−CD62L− T cells (Chan senting cells (APCs) as both β2m-associated and free heavy chain et al., 2005). A higher proportion of CD28−CD4 T cells express (FHC) species (Kollnberger et al., 2002, Payeli et al., 2012; Bird KIR3DL2 than the related KIR3DL1 in both healthy controls and et al., 2003). B27 has a reactive cysteine at position 67 which results spondyloarthritis (SpA) patients (Chan et al., 2005). CD28−CD4 in an increased propensity to form FHC species including dimers T cells have been implicated in the pathogenesis of both rheuma- at the cell surface. We have shown that KIR3DL2 binds to B27 toid arthritis and SpA (Warrington et al., 2001; Chan et al., 2005; FHC forms including dimers (Kollnberger et al., 2002). In trans- Raffeiner et al., 2005). fected cells, cell surface B27 heavy chain dimers and other FHC Promoter hypomethylation and an active histone signature species form from recycling β2m-associated B27 in an endoso- in KIR-expressing cells are associated with KIR3DL2 gene tran- mal compartment (Bird et al., 2003). Formation of B27 FHC is scriptional activity but factors which specifically control expres- increased when β2m-associated B27 is suboptimally loaded with sion are unclear (Chan et al., 2003; Santourlidis et al., 2008; Zhang peptide (Bird et al., 2003). The extent to which pMHC stabil- et al., 2011). ity and recycling contribute to formation of B27 FHC species in vivo is unknown. B27 heavy chain dimer tetramers but not β2m- HLA CLASS 1 LIGANDS FOR KIR3DL2 associated B27 tetramers bind to KIR3DL2 (Kollnberger et al., NKAT4 or KIR3DL2*001 was originally shown to bind specifically 2002, 2007). By contrast, both B27 heavy chain dimers and β2m- to HLA-A3 and -A11 but not -A1, -A2, and -A24 (Wagtmann associated B27 bind to KIR3DL1 (Kollnberger et al., 2002, 2007). et al., 1995; Dohring et al., 1996; Pende et al., 1996). It was KIR3DL2 ligation by B27 FHC inhibits leukocyte production of later shown that KIR3DL2*001 binding to tetramerized peptide IFNγ and promotes NK and T cell survival (Chan et al., 2005; MHC (pMHC) complexes of HLA-A3 and -A11 was critically Bowness et al., 2011). Moreover B27 FHC stimulate IL2 produc- dependent on the sequence of complexed viral peptide, with the tion by KIR3DL2CD3ε-transduced Jurkat reporter T cells (Payeli RLRAEAQVK EBV/EBNA3A (603–611) epitope promoting inter- et al., 2012). KIR3DL2 interaction with HLA-B27 FHC forms is action (Hansasuta et al., 2004). As with other KIR-HLA class 1 inhibited by B27-dimer specific antibodies (Payeli et al., 2012). By interactions positions 7 and 8 of complexed peptide were shown contrast with KIR binding to classical HLA class 1 which depends to be critical for promoting pMHC complex HLA-A3 and -A11 on the sequence of complexed peptide, KIR3DL2 binding to B27 binding to KIR3DL2. The exact role of bound peptide in pMHC heavy chain forms is independent of the sequence of bound pep- complex recognition by three domain KIRs remains unclear. KIR tide (Kollnberger et al., 2007). By contrast, it is unclear whether binding to class 1 distinguishes self from lack of self as may happen B27 FHC interact functionally with KIR3DL1. when class 1 is down-regulated by virus infection. It is unknown whether KIR3DL2 interacts functionally with Studies on interactions of two domain KIRs with pMHC have ligand as a dimer or monomer. Since there is no polymorphic shown that KIR-expressing NK cells respond more readily to variation in this region it is plausible that dimerization is impor- changes in peptide than to changes in HLA class 1 expression tant for receptor function. The inhibition of KIR3DL2 interaction (Fadda et al., 2010). Tumors and viruses do not always necessarily with HLA-B27 by the heavy chain-specific MAb HC10 suggests down-regulate HLA class 1 substantially but may change peptide that this particular KIR may recognize common shared features repertoire. Under these circumstances peptide selectivity confers of HLA class 1 heavy chains (Kollnberger et al., 2007). KIR3DL2 NK cells with an additional recognition mechanism. KIR inhibi- dimerization could increase the avidity of interaction with B27 tion of NK function by pMHC is highly sensitive to the presence of heavy chains. KIR3DL1 binds more strongly to β2m-associated antagonist peptides which do not induce inhibition (Fadda et al., HLA-B27 tetramers than B27 dimer tetramers (Kollnberger et al., 2010). The effect of antagonist peptides in uncoupling KIR cluster- 2007). Weaker interaction of KIR3DL1 with B27 FHC compared ing from NK inhibition dominates over effects of agonist peptides to KIR3DL2 could offer one possible explanation for why there which promote inhibition. This could enable NK cells to discrimi- is no clear association of KIR3DL1 with SpA. KIR3DL1 has also nate and respond to small changes in peptide repertoire bound by been shown to bind to common shared features of HLA class 1. HLA class 1 at the cell surface during infection. The recent structure of KIR3DL1 in complex with HLA-B57 sug- In NK development strong class 1 ligands for KIR promote gests that the D0 domain may bind to more conserved regions of or “license” NK cells with better effector function. Most of the HLA class 1 whereas the D1 and D2 domains provide allelic and identified peptides which promote binding to three domain KIRs peptide-specific contacts (Vivian et al., 2011). The D0 domain acts are from pathogens and few self peptides which promote strong to enhance KIR3DL1*001 binding to HLA class 1. Phe9, Trp13, His binding have been identified (Kollnberger et al., 2007). KIR3DL2- 29, Phe34 amino acids in the D0 domain of KIR3DL1*001 bind expressing NK cells in HLA-A3+ individuals have poor effector loops formed by amino acids 14–18 and 88–92 of HLA-B*5701.

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These loops are highly conserved between different HLA class 1 (Brown et al., 1996). These disorders, characterized by primary alleles. By analogy the D0 domain of KIR3DL2 could have a role inflammation of the sacroiliac joint, include reactive arthritis, to play in recognition of HLA-B27 and other HLA class 1 heavy early onset enthesitis related arthritis (ERA),psoriatic arthritis and chains. Notably in KIR3DL2 the D0Trp13 is substituted by a his- IBD-associated enteropathic arthritis and are typified by ankylos- tidine. The relative contributions of these and other residues to ing spondylitis (AS). GWAS studies have identified genes involved binding of KIR3DL2 to B27 FHC forms and other HLA class 1 in regulation of IL17 production including the transcription fac- remain to be determined. tor STAT3 and the IL23 receptor (IL23R) as having important We propose that multimeric forms of B27 heavy chains which roles in AS (Reveille et al., 2011). IL17 plays an important role in include B27 dimers interact more strongly with KIR3DL2 and diverse autoimmune disorders including rheumatoid arthritis and other immune receptors than other HLA class 1. We have shown SpA (Wendling et al., 2007; Shen et al., 2009; Bowness et al., 2011). that multimeric FHC forms and heavy chain dimers of B27 bind IL17 has multiple proinflammatory actions which include stimu- more strongly to the leukocyte immunoglobulin-like receptor lating TNFα production and enhancing the recruitment of other LILRB2 than β2m-associated HLA-B27 and other HLA class 1 proinflammatory leukocytes including neutrophils to the sites of (Giles et al., 2012). Stronger anti-apoptotic and functional effects inflammation (Jovanovic et al., 1998; Laan et al., 1999). resulting from B27 FHC forms binding to KIR3DL2 compared We observe increased proportions of NK and CD4 T cells with other HLA class 1 ligands could explain why HLA-B27 and expressing KIR3DL2 in the peripheral blood and peripheral joints not other HLA class 1 is associated with SpA. of patients with SpA (Chan et al., 2005; Bowness et al., 2011). Patients with B27+ juvenile ERA demonstrated increased pro- KIR3DL2 FUNCTION portions of CD4 T cells but not NK cells expressing KIR3DL2 Although KIR3DL2 ligation on NK cells inhibits IFNγ and cyto- compared to B27 negative healthy and disease controls. By con- toxic function, its effects on T cell function are less clear. KIR3DL2 trast, patients with established AS had greater proportions of ligation inhibits target cell lysis by the TALL104 cell line (Brando both NK and CD4 T cells expressing KIR3DL2 compared to et al., 2005). However, both antibody and HLA class 1 ligation B27 negative controls. This suggests that KIR3DL2 expression of KIR3DL2 have been reported to have no effect on CD8 T cell by CD4 T cells may have a role in initial inflammation in B27- cytokine secretion and cytotoxicity under certain circumstances associated arthritis. By contrast, KIR3DL2-expressing NK cell (Pende et al., 1996). This is consistent with the notion that func- subsets may be involved in perpetuating inflammation. This is tional effects of KIR on T cells are dependent on the differentiation also supported by our observations of greater proportions of and/or activation status of cells expressing these receptors. The KIR3DL2-expressing CD4 T cells in patients with B27+ reactive contribution of allelic variation to KIR3DL2 recognition of differ- arthritis compared to patients with more established disease (Bow- ent HLA class 1 is unknown. In addition nothing is known about ness et al., 2011). KIR3DL2+ NK cells from patients expressed the effect of allelic variation on antibody recognition of KIR3DL2. high levels of perforin and the CD38 activation marker and The large number of protein-encoding polymorphic variants of were enriched for expression of the β7 integrin suggesting a KIR3DL2 suggests that the list of class 1 ligands for this receptor mucosal and possibly gut origin (Chan et al., 2005). More- is by no means exhaustive. over NK cells from patients were more cytotoxic toward targets than cells from controls (Chan et al., 2005). However, the rel- INNATE LIGANDS FOR KIR3DL2 ative contribution of KIR3DL2-expressing and NK cells lacking Natural killer cells express a range of toll-like receptors includ- KIR3DL2 expression to the increased cytotoxicity was not deter- ing TLR3 and TLR9 and are rapidly activated by TLR binding to mined. NK cells stimulate chemokine and MMP production by PAMPs (reviewed in Marcenaro et al., 2011). Binding of poly I:C fibroblasts and are themselves sources of chemokines-like IL8 and CpG-oligodeoxynucleotide (ODN) PAMPs to their respec- (Raffeiner et al., 2005; Chan et al., 2008; Fauriat et al., 2010). Apart tive TLR, TLR-3 and -9 both promotes NK cytokine release and from increased cytotoxicity it is also possible that KIR3DL2+ increases cytotoxicity. Cell surface KIR3DL2 is down-modulated expressing NK cell subsets in B27+ SpA patients enhance inflam- by binding to CpG-ODN and subsequently KIR3DL2 transports mation through activation of key coordinating cells such as bound CpG-ODN to endosomes where TLR9 is ligated (Sivori fibroblasts. et al., 2010). KIR3DL2 and KIR3DL1 bind to CpG-ODN via their We and other authors have also shown increased expression D0 domain. Although both KIR3DL1 and KIR3DL2 bind in this of HLA class 1 heavy chains and B27 heavy chain dimers on the way, KIR3DL2 modulation is particularly strong upon cell expo- surface of B27+ AS patient leukocytes (Kollnberger et al., 2002; sure to CpG-ODN and KIR3DL2-expressing NK Cells are more Payeli et al., 2012; Tsai et al., 2002; Raine et al., 2006). We pro- responsive to TLR9-mediated activation. This selective effect of pose that expansion of KIR3DL2-expressing NK and CD4 T cells CpG-ODN on KIR3DL2 could be related to dimerization of the in AS patients is driven by higher avidity interactions with B27 molecule and/or differences in the cytoplasmic tail compared to FHCs formed in disease. Stronger interactions with KIR3DL2 the other three domain KIRs. could result either from B27 FHC forms binding more strongly or higher levels of expression of B27 ligands compared to other KIR3DL2 EXPRESSION IN DISEASE HLA class 1. THE ROLE OF KIR3DL2 IN SPONDYLOARTHRITIS Increased expression of HC10-reactive heavy chains has also HLA-B27 is strongly associated with a group of inflammatory been associated with psoriatic arthritis (Lan et al., 2004). Notably arthritides collectively known as the spondyloarthritides/SpA both B27+ and B27− psoriatic arthritis patients demonstrated

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increased expression of heavy chains on peripheral blood mono- We have shown that cell lines expressing HLA-B27 FHC pro- cytes compared to controls, with B27− patients showing signifi- mote the survival of KIR3DL2 CD4 T cells secreting IL17 (Bowness cantly higher levels of expression compared to B27+ (Lan et al., et al., 2011). The Th1 cytokine IFNγ negatively regulates IL17 pro- 2004). Although this hypothesis is attractive, direct evidence for duction both by directly inhibiting Th17 cell production and also the physiological relevance of KIR interactions with B27 and inhibiting IL23 production by APCs (Mills, 2008; Sheikh et al., other HLA class 1 heavy chains in vivo remains to be determined. 2010). In addition to promoting leukocyte survival, KIR3DL2 If KIR3DL2-expressing leukocytes are also involved in psoriatic ligation by B27 could also promote disease by limiting produc- arthritis, it is possible that interactions with other class 1 heavy tion of Th1 cytokines, thus skewing leukocytes toward production chains could have a similar effect to B27 in promoting the survival of IL17. If B27 FHC are indeed stronger ligands for KIR3DL2 and differentiation of inflammatory leukocytes in these disorders. than other β2m-associated HLAclass 1, stronger binding of B27 to KIR3DL2-expressing CD4 T cells are enriched for expression KIR3DL2 could have a more pronounced effect on inhibition of of Th17 phenotypic markers and particularly IL23R expression IFNγ production than other HLA class 1. (Bowness et al., 2011). Notably, although comprising just 15% KIR3DL2 ligation by B27 also promotes the survival of NK of all peripheral blood CD4 T cells in SpA, KIR3DL2+CD4 cells and inhibits their production of IFN-γ (Chan et al., 2005). T accounted for 60% of all IL23R-expressing CD4 T cells. B27 interactions with KIR3DL2 could thus have a role in promot- KIR3DL2-expressing CD4 T cells are also enriched for IL23R ing the expansion of the increased proportions of KIR3DL2+ NK expression in healthy B27-controls where they constituted 30% cells observed in B27+ patients with SpA. The demonstration of of all IL23R-expressing CD4 T cells. Moreover, KIR3DL2+CD4 T a functional interaction between KIR3DL2 and HLA-B27 raises cells accounted for the majority of the increase in IL17 produc- the possibility that this interaction could be involved in the devel- tion by peripheral blood CD4 T cells in SpA patients compared to opment of NK effector function or licensing in SpA and other healthy and disease controls (Bowness et al., 2011). diseases with B27 involvement. The greater expression of KIR3DL2 on CD4 T cells compared No specific alleles of KIR3DL2 have been associated with SpA to other KIR allowed us to directly FACS sort this population from (Harvey et al., 2009). These studies do not exclude the possibility peripheral blood and measure cytokine production by short term that a rare allelic variant of KIR3DL2 is associated with disease. cultures stimulated with anti-CD3, anti-CD28, and anti-CD2. We found a similar effect of B27-expressing APC in promoting the KIR3DL2 CD4 T cells from SpA patients consistently produced survival of KIR3DL2-expressing CD4 T cells from a wide range of more IL17 than the same subset isolated from controls. IL17 pro- control and SpA subjects. This suggests that KIR3DL2 polymor- duction by KIR3DL2 CD4 T cell subsets from patients and controls phism has little effect on the interaction with B27 FHC, although was further promoted by stimulation in the presence of the Th17 KIR3DL2 allelic variation could affect the strength of interaction. cytokines IL23 and IL1 (Bowness et al., 2011). However, stimu- lation with Th17 cytokines promoted a greater increase in IL17 THE ROLE OF KIR3DL2 IN SÉZARY’S SYNDROME production by the KIR3DL2 CD4 T cell subset from SpA patients Apart from SpA, KIR3DL2 expression delineates both circulating compared to increases in IL17 production by the same subset in and infiltrating T cell lymphoma cells in Sézary’s syndrome (SS; controls. Musette et al., 2003; Poszepczynska-Guigne et al., 2004). SS is not The observation of production of IL17 by KIR-expressing CD4 associated with HLA-B27 and the ligand/ligands for KIR3DL2 in T cells contradicts previous observations where KIR-expressing this disease are unknown. SS is an erythrodermic, aggressive, cuta- CD4 T cells were shown to produce only small levels of Th17 neous T-cell lymphoma characterized by a malignant T-cell clone cytokines (van Bergen et al., 2004). It is possible that previous that localizes in the blood and skin. Expansion of SS T cells could be work with KIR-expressing CD4 T cell lines and clones selected for driven by innate ligands such as bacterial CpG DNA, or KIR3DL2 outgrowth of Th1 cells and IL17 producing cells could have been expression could occur as a secondary consequence of T cell trans- missed. formation. The demonstration of expansions of non-lymphoma We did not observe significant increases in IL23R expression T cells expressing KIR3DL2 in SS patients suggests that the latter on CD4 T cells from SpA patients lacking KIR3DL2 expres- possibility is unlikely. SS T cells and KIR3DL2-expressing CD4 T sion (Bowness et al., 2011). We consistently observe expansion cells in SS patients have a restricted Vβ TCR repertoire suggest- of KIR3DL2-expressing CD4 T cells in B27+ SpA patients and ing antigen-driven expansion of these cells (Ortonne et al., 2006). B27+ but not B27-healthy controls. The increase in KIR3DL2 KIR3DL2 expression has been proposed to be induced on SS T expression on CD4 T cells in the peripheral blood of B27+ healthy cells by bacterial exposure. KIR3DL2 expression has also been controls is intermediate between healthy B27− controls and B27+ reported to be up-regulated on T cells in adult T cell leukemia SpA patients (Bowness et al., 2011). This strongly suggests that which is strongly associated with HTLV-1 infection and associated B27 interactions with KIR3DL2 have a central role to play in SpA. infective dermatitis (Obama et al., 2007). KIR3DL2 interactions with B27 could also have a role to play in T cells from patients with SS demonstrate constitutive phos- other diseases where HLA-B27 has been shown to play a role. In phorylation of pSTAT3 and secrete IL17 (Ciree et al., 2004; van der addition, the level of surface expression of HLA-B27 may have Fits et al., 2012). KIR3DL2 ligation by an as yet uncharacterized a key role in determining progression toward arthritis. Indeed ligand may promote expansion of T cells in SS. Candidate ligands increased levels of both β2m-associated and FHC forms of B27 could be CpG DNA or HLA class 1 heavy chains. Alternatively, have been associated with disease (Cauli et al., 2002; Tsai et al., increased KIR3DL2 expression could result from T cell activation 2002; Raine et al., 2006). independently of binding to ligand. SS T cells may also have a

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FIGURE 1 | Hypothetical role of KIR3DL2 ligand interactions in could bind more strongly to KIR3DL2 than β2m-associated HLA class 1. B27 inflammation. KIR3DL2 is expressed as a disulphide-bonded dimer with D0, FHC are predicted to bind to KIR3DL2 via the D0 domain. (4) KIR3DL2 binding D1, D2 immunoglobulin-like domain organization and two cytoplasmic ITIM to ligand inhibits activation induced cell death driven by TCR/NK receptor motifs. (1) KIR3DL2 expression is induced by T cell activation and/or NK ligand interactions, promoting the survival of pathogenic Th17 and NK cell differentiation. (2) Bacterial infection may promote formation of B27 dimers subsets in disease. The D0 domain of KIR3DL2 also binds bacterial CpG DNA. (B272) and free heavy chains (FHC) by enhanced recycling of β2m-associated CpG DNA internalized by KIR3DL2 could costimulate NK and T cell via TLR9 HLA class 1 by antigen presenting cells (APC). (3) B27 FHC including B272 ligation (1 and 4). role in neutrophil recruitment to inflammatory sites in the skin in potential transcription binding sites between KIR3DL2 and other SS as neutrophil recruitment correlates with IL17 production by KIR genes and the large size of the KIR3DL2 gene locus sug- these cells. Although IL17 itself is not essential, IL21 produced by gest unique transcriptional control. KIR3DL2 ligands include SS T cells has an important role to play in the maintenance of this HLA-A3 and -A11, HLA-B27 FHC dimers and other FHCs and subset (van der Fits et al., 2012). CpG-ODN. The influence of KIR3DL2 dimerization on ligand KIR3DL2 CD4 T cells in SpA have a highly activated pheno- binding remains to be determined. KIR3DL2 expression is up- type suggesting that expression may be induced by chronic T cell regulated on activated CD4 T cells and NK cells in SpA and activation (Chan et al., 2005). B27+ reactive arthritis is associated circulating and T cell lymphoma cells in SS. Since both disor- with gram-negative intracellular bacterial infection. Evidence of ders are associated with bacterial infection, it is possible that subclinical gut inflammation in SpA patients and the association bacterial exposure in general may have a role in promoting of HLA-B27 with inflammatory bowel disease also link SpA with the expansion of KIR3DL2-expressing T cells. The enrichment bacterial infection (Ciccia et al., 2009; Brown, 2011). One possibil- of expression of Th17 phenotypic markers and production of ity is that KIR3DL2 expression in SpA and SS is linked to bacterial IL17 by peripheral KIR3DL2-expressing CD4 T cells suggests a activation of leukocytes. unique role for KIR3DL2 expression in the differentiation of Th17 cells. CONCLUDING REMARKS KIR3DL2 is a highly polymorphic framework KIR gene. Figure 1 ACKNOWLEDGMENT summarizes how KIR3DL2 expression and ligation may con- Simon Kollnberger and Jacqueline Shaw are supported by Arthritis tribute to immune regulation and inflammation. Differences in Research UK.

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Vivian, J. P., Duncan, R. C., (2001). CD4+, CD28− T cells in uremia patients. DNA Cell Biol. 30, ligands and function of the killer cell Berry, R., O’Connor, G. M., rheumatoid arthritis patients com- 179–186. immunoglobulin-like receptor KIR3DL2 Reid, H. H., Beddoe, T., et al. bine features of the innate and in health and disease. Front. Immun. (2011). Killer cell immunoglobulin- adaptive immune systems. Arthritis 3:339. doi: 10.3389/fimmu.2012.00339 like receptor 3DL1-mediated recog- Rheum. 44, 13–20. Conflict of Interest Statement: The This article was submitted to Frontiers in nition of human leukocyte antigen B. Wendling, D., Cedoz, J.-P., Racadot, authors declare that the research was NK Cell Biology, a specialty of Frontiers Nature 479, 401–405. E., and Dumoulin, G. (2007). Serum conducted in the absence of any com- in Immunology. Wagtmann,N.,Biassoni,R.,Cantoni,C., IL-17, BMP-7, and bone turnover mercial or financial relationships that Copyright © 2012 Shaw and Kollnberger. Verdiani, S., Malnati, M. S.,Vitale, M., markers in patients with ankylos- could be construed as a potential This is an open-access article distributed et al. (1995). Molecular clones of the ing spondylitis. Joint Bone Spine 74, conflict of interest. under the terms of the Creative Commons p58 NK cell receptor reveal immuno- 304–305. Attribution License, which permits use, globulin-related molecules with dive- Zhang, L., Dai, Y., Wang, L., Peng, Received: 04 May 2012; accepted: 23 distribution and reproduction in other rsity in both the extra- and intracel- W., Zhang, Y., Ou, Y., et al. (2011). October 2012; published online: 16 forums, provided the original authors and lular domains. Immunity 2, 439–449. CpG array analysis of histone H3 November 2012. source are credited and subject to any Warrington, K. J., Takemura, S., lysine 4 trimethylation in periph- Citation: Shaw J and Kollnberger copyright notices concerning any third- Goronzy, J. J., and Weyand, C. M. eral blood mononuclear cells of S (2012) New perspectives on the party graphics etc.

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